Cigarette filters disintegrate relatively slowly and are therefore an annoyance to broad sections of the population in places where there is much smoking.
For most cigarette filters, fibrous cellulose acetate is being used today having an acetyl number between 53 and 57% (such as for example described in U.S. Pat. No. 2,953,837. The numerical values cited in this patent, namely 38% to 41% for the acetyl content, correspond to the above mentioned values of 53 to 57% for the acetyl number).
Compared with other polymers, in particular synthetic ones, such a cellulose acetate is indeed biodegradable, but the time spans after which cigarette filters of such a fibrous material have disappeared at least optically under the action of environmental influences are too long in today's estimation.
German patent application 40 13 293 and German patent application 40 13 304 describe cigarette filters which under the action of environmental influences are decomposable relatively quickly, but these cigarette filters consist of a section of a transverse-axially compacted fiber skein of fibers of spun PHB (polyhydroxybutyric acid) or a copolymer of PHB and PHV (polyhydroxyvaleric acid). At present, such polymers are not being used for the manufacture of filter tow and tobacco smoke filter elements, or at least not to a noteworthy extent, which may be due to
From German patent application 39 14 022, new plastic materials easily biodegradable are known by composting and their use for the manufacture of sheaths/containers for oil lamps, eternal light oil candles, composition oil lamps, other grave lamp models, sacrificial lamps and foils. As plastic materials there are named in German disclosure 39 14 022 those materials based on cellulose esters, such as cellulose acetate, with additions, such as polyester, citric acid esters, phosphoric acid esters and organic iron compounds. However, German patent application 39 14 022 gives no indication of the possibility of accelerating the biodegradation of filter tow and tobacco smoke filter elements. Besides, the formulation described in German patent application 39 14 022 is not suitable for the production of filter tow and tobacco smoke filter elements because of too high a proportion of plasticizer in the cellulose acetate.
Recently the microbiological decomposition of cellulose acetate under a variety of environmental conditions has been described in scientific publications. Thus, for example, the publication DEGRATION OF CELLULOSE ACETATE FILTERS IN AQUEOUS SYSTEMS by Eberhard Teufel and Rolf Willmund, read as a paper at the "JOINT MEETING OF SMOKE AND TECHNOLOGY GROUPS" of the CORESTA on Sep. 16, 1991 in Utrecht, Netherlands, describes the mechanism of the biological degradation of cellulose acetate. Another publication, namely "THE FATE OF CELLULOSE ACETATE IN THE ENVIRONMENT: AEROBIC BIODEGRADATION OF FILTER TOW FIBERS" by Charles M. Buchanan, Robert M. Gardner, Ronald J. Komarek and David Strickler, read as a paper at the "TOBACCO CHEMIST RESEARCH CONFERENCE" on Oct. 22, 1991 in Asheveille, N.C., U.S.A., describeds the aerobic degradation of cellulose acetate.
Another publication, namely "Effects of Natural Polymer Acetylation of the Anaerobic Bioconversion to Methane and Carbon Dioxide", by C. J. Rivard et al, published in Applied Biochemistry and Biotechnology, Volume 34/35, 1992, pages 725 to 736, describes the anaerobic degradation of cellulose acetate.
It is evident from all three above-mentioned publications that aerobic as well as anaerobic decomposition of cellulose acetate takes place faster with decreasing acetyl number. The above publications, however, give no hint of the possibility of accelerating the biodegradation of filter tow and tobacco smoke filter elements consisting of cellulose acetate; especially the two last-named publications show that the biodegradation of cellulose acetate can be accelerated by lowering its acetyl number, but they say nothing about how this could be technically realizable for filter tow and tobacco smoke filter elements of cellulose acetate fiber material.
A synoptic view of the prior art shows, therefore, that for filter tow and tobacco smoke filter elements consisting of cellulose acetate fiber materials as well as tobacco smoke filter elements made of such filter tow, no solution for accelerating their biodegradation is as yet known.